1. Field of the Invention
This invention relates to a circuit and a method for generating a bandgap reference voltage for integrated circuits.
More particularly this invention relates to providing bandgap reference voltage which is temperature, process and power supply independent. In addition, this invention relates to the ability to generate lower reference voltages which are compatible with the advances in integrated circuits.
2. Description of Related Art
FIG. 1 shows a prior art bandgap reference circuit. A differential amplifier is made up of two p-channel metal oxide semiconductor field effect transistors PMOS FETs MP1180 and MP2150. It is also made up of the two n-channel metal oxide semiconductor FETs MN1170 and MN2160. Finally, the differential amplifier is made up of a current source 135 which connects to the common sources of the two NMOS FETs of the differential amplifier and sinks the current from them.
FIG. 1 also shows a first input path that drives the first differential input Vb 165. The first input path contains resistor R3120 and PN diode Q2130. PN diode Q2130 is constructed from a PNP bipolar junction transistor, BJT, Q2130. The BJT 130 has its base and collector tied in common to ground 140. The emitter of Q2130 is tied to the resistor R3120. In the prior art in FIG. 1, some implementations utilize multiple PN diodes in the first input path as represented by 145.
FIG. 1 also shows a second input path that drives the second differential input Va 175. The second input path contains PN diode Q1125. PN diode Q1125 is constructed from a PNP bipolar junction transistor, BJT, Q1125. The BJT 125 has its base and collector tied in common to ground 140. The emitter of Q1125 is tied to the input Va 175.
FIG. 1 also shows a first feedback path that contains a first feedback resistor, R2110. This R2 resistor is connected between the first differential input Vb 165 and the differential output VBP 155.
FIG. 1 also shows a second feedback path that contains a second feedback resistor, R1115. This R1 resistor is connected between the second differential input Va 175 and the differential output VBP 155.
FIG. 1 also shows a third PMOS FET, MP3190. This device is used to drive the differential output VBP 155. Also, the PMOS FET, MP3190 is used to isolate the differential output VBP 155 from the internal differential amplifier node 171. MP2150 and MP1180 are a current mirror. They are uses as the active load of MN2160 and MN1170.
U.S. Pat. No. 6,281,743 B1 (Doyle) xe2x80x9cLow Supply Voltage Sub-Bandgap Reference Circuit xe2x80x9d describes a reference circuit which results in a reference voltage which is smaller than the bandgap voltage of silicon. The circuit is temperature compensated.
U.S. Pat. No. 6,204,724 (Kobatake) xe2x80x9cReference Voltage Generation Circuit Providing a Stable Output Voltagexe2x80x9d discloses a reference voltage generation circuit which utilizes two current mirrors circuits. This invention produces a stable output voltage.
U.S. Pat. No. 5,796,244 (Chen, et al.) xe2x80x9cBandgap Reference Circuitxe2x80x9d discloses a voltage reference circuit, which is incorporated within an integrated circuit and which minimizes currents into the substrate.
U.S. Pat. No. 5,900,773 (Susak) xe2x80x9cPrecision Bandgap Reference Circuitxe2x80x9d discloses a precision bandgap reference circuit. The circuit has an output stage which is biased with Proportional To Absolute Temperature (PTAT) current which is well controlled.
U.S. Pat. No. 6,150,872 (McNeill, et al.) xe2x80x9cCMOS Bandgap Voltage Referencexe2x80x9d discloses a bandgap reference circuit, which uses Proportional To Absolute Temperature (PTAT) voltage. The circuit can generate voltages below 1.24 volts. The invention utilized a start-up circuit to force the reference circuit into a known state.
It is the objective of this invention to provide a circuit and a method for generating a bandgap reference voltage.
It is further an object of this invention to provide a bandgap reference circuit and method which provide a stable bandgap reference voltage which is immune to temperature, process and power supply variations.
It is further an object of this invention to provide the ability to generate lower reference voltages which are compatible with the advances in integrated circuits.
The objects of this invention are achieved by a bandgap reference circuit made up of a differential amplifier whose two inputs are compared to produce a difference signal and whose output is fed back to two input resistors of different values, a first differential input path which contains a first input bias resistance one end of which is connected to the first differential input, the other end of this first bias resistance is connected to the P-side of a first diode whose N-side is connected to ground, a second differential input path which contains a second input bias resistance one end of which is connected to the second differential input, the other end of this second bias resistance is connected to the P-side of a second diode whose N-side is connected to ground, a path parallel to said second differential input path which contains a capacitor connected between the second differential input and ground, a first feedback path from the differential output to a first feedback resistor whose other side is connected to said first differential input, a second feedback path from the differential output to a second feedback resistor whose other side is connected to the second differential input, and a differential output node which is driven by an MOS FET.
The bandgap reference circuits differential amplifier contains two P-channel metal oxide semiconductor P-MOSFET devices whose sources are connected to the Vdd supply voltage and are used as load devices and for current mirroring, two NMOS FETs whose inputs are connected to the two inputs which are to be compared, and a current source whose constant current flows from the commonly connected sources of said two NMOS FETs to ground. The bandgap reference circuit""s first differential input path contains a first bias resistance which is composed of two series connected parts, a constant part and a variable part. The bandgap reference circuit""s variable part of the first input bias resistance is a function of the resistance of the first feedback path. The bandgap reference circuits second differential input path contains a second bias resistance which is composed of two series connected parts, a constant part and a variable part.
The bandgap reference circuit""s variable part of the second input bias resistance is a function of the resistance of the second feedback path. The bandgap reference circuit""s path parallel to the second differential input path which contains a capacitor C which is connected between the second differential input and ground. The bandgap reference circuit""s first feedback path contains a first feedback resistance. The bandgap reference circuit""s first feedback resistance has a design value which is a function of said variable component of the first input bias resistance. The bandgap reference circuit""s second feedback path contains a second feedback resistance. The bandgap reference circuit""s second feedback resistance has a design value which is a function of the variable component of the second input bias resistance. The bandgap reference circuit""s differential output is driven by a third PMOS FET device.